Rice is one of the main grain crops on which the life of human being depends, provides staple food for nearly one half of the world population. In China, rice stands first among all grain crops in production and accounts for 60% of grain ration consumption of Chinese residents; nearly half of the farmers are engaged in rice production. Accordingly, rice plays a leading role in Chinese food crops. With the increasing growth of global population (the population growth rate of rice-consuming countries is faster than the average growth rate of the world population) and rapid development of industrialization and urbanization as well as damages caused by natural disasters and the like, there is an decreasing trend in rice paddies, causing a pressing conflict between the global rice supply and demand. How to produce more food on less rice paddy lands so as to ensure the safe supply of rice? It is an urgent problem we are facing and must overcome. However, the rice output under large-scale production is generally very low. According to an investigation conducted by the Food and Agriculture Organization of the United Nations (FAO) in 1999, the world average rice yield per unit area is only 3.8 t·ha-1 (6.3 t·ha-1 in China). For this end, China has put forward the rice breeding project for super high yield (the super rice breeding project) in recent 30 years to develop the yield potential of high yield varieties and thereby, substantially improving the rice yield. Grain weight and grain number per panicle are important factors affecting crop production, and increasing grain size, grain weight or grain number per panicle is an effective approach to improve rice yield. Moreover, the length of grain is an important morphological character that decides the rice quality. As to the biologists and agronomists, it is a goal most worth pursuing to raise both production and quality of rice.